Can you tell me the differences bewteen different RAID types?

Question

RAID

Answer 1

Raid 0 is also known as "stripping". It allows the hdd controller to put one bit on the first drive and the second bit on the second drive. This allows for faster drive access.

Raid 1 is aka "mirroring". The same bit gets written to both drives, so that if one drive fails, the other drive is a full backup.

Raid 5 is the most commonly used raid these days. It uses a "parity" drive so that if one drive fails, all the data remains in check with the remain drives, (minimum of 3 drives required).

More here:
http://www.ebabble.net/html/types.html

Note: with the speed of hard drives as they are now, use of Raid 0 is a waste.

Raid 1 is still used for simple redundancy on less critical systems.

Raid 5, as noted, is the most commonly used, as most decent server hardware supports "hot swappable" drives, so if one fails, it can be removed and a good one put in its place without ever having to take the server down.

Raid 51, (a combination of Raid 5, with a second equal Raid 5 setup mirroring the first), is used for mission critical systems.
You might see these used in military or the medical field. The price of disk space is cheap nowadays, so drive redundancy is much more prelevant and elaborate.

Answer 2

There are essentially 5 types of RAID:

RAID0 - Stripe Array: In this an array of hard disks is used to split up the data to be written at bit level and written across the disks. For ex: to write one byte across an array of two disks, 4 bits are written on each. Requires atleast two identical disks. Performance is superb but offers no protection against data-loss. Capacity = size X number of disks.

RAID1 - Mirror Array: In this an array of hard disks is used to mirror each others contents. For ex: if you write on byte to one disk, its automatically written to the other disk/s. Requires atleast two identical disks. Performance may suffer but protection is 100%. Capacity = size of any one disk.

RAID0+1 - Striping & Mirroring: In this an array of hard disks is used to setup both RAID0 and 1. Requires atleast 4 identical hard disks. While each pair is in RAID0 config, the pairs themselves are in RAID1 config. Performance is great, protection is great, but expensive and complicated to setup.

JBOD - Just a Bunch of Disks: This is not really a RAID, but very popular. This is similar to RAID0, but the bytes are not split at bit level across the drives. Instead, the bytes start filling up the other drives only when the previous one is full. Requires atleast two disks of any capacity. For ex: in a JBOD array of 20, 30 GB disks, the 30 GB wont have any data on it until the 20GB is filled up. Performance is not as good as RAID0, protection is absent, but makes sense if lots of files are being accessed simultaneously. The drives are reponsible for individual files stored on them. (in RAID0, the heads move in tandem, thus 1 file at a time).

RAID5: This is an advanced version of RAID0+1. This stripes the data at bit level across the drives and instead of mirroring the drives, it uses a drive to just store the parity data. In the event of an error (disk crash), the parity data can be used to re-build the lost data. Requires atleast 3 hard disks.